1. Field of the Invention
The present invention relates to a method of and an apparatus for continuously manufacturing molded slide fastener coupling elements of thermoplastic synthetic resin.
2. Prior Art
Continuous molded coupling elements for slide fasteners have found widespread use since they are available in a variety of shapes and colors, have coupling heads of an ideal configuration, render a resultant slide fastener mechanically strong, are relatively light, and can be manufactured at a high rate of production and hence inexpensively. Such molded coupling elements are produced by first molding a strip of coupling element blanks, and then folding the strip of blanks about its longitudinal axis into a U-shape while being heated by high-frequency heating, which may be followed by ultrasonic bonding of legs of formed coupling elements. When these two processing steps are combined together, the overall rate of production of coupling elements becomes reduced since the step of high-frequency heating or ultrasonic bonding takes much more time than the step of molding the strip of coupling element blanks. To cope with this difficulty, it has been proposed to carry out these two steps independently on separate apparatus such as disclosed in U.S. Pat. Nos. 4,025,277 patented May 24, 1977 and 4,210,985 patented July 8, 1980. The former U.S. patent discloses an apparatus for folding and fusing a strip of coupling element blanks, the apparatus including a heater for heating the strip of coupling elements blanks which has been cooled down after being discharged from a molding apparatus as disclosed in the latter U.S. patent. The proposed process is also disadvantageous in that an additional time is required to heat the strip of blanks again for folding and heat-setting or bonding the latter, resulting in a reduction in the rate of manufacture of molded slide fastener coupling elements.